Upgrade to protoc-gen-go from google.golang.org/protobuf

[Mistic92]

Please update it to work with gomodules and latest release of protoc. Currently I'm getting

Compiling protobuf definitions
--go_out: protoc-gen-go: plugins are not supported; use 'protoc --go-grpc_out=...' to generate gRPC

Also previously I had to add option go_package = "./"; to proto file.

[johanbrandhorst]

Hi. This error is happening because you have a newer version of protoc-gen-go installed locally. This repository still uses github.com/golang/protobuf. You can install the correct version using go install github.com/golang/protobuf/protoc-gen-go in the root of this repository.

We should however update to using protoc-gen-go from google.golang.org/protobuf, so I'll keep this issue open.